The water-soluble peridinin--chlorophyll a--proteins (sPCP) from three symbiotic dinoflagellates, Symbiodinium microadriaticum, S. kawagutii and S. pilosum, have been analysed for their quaternary structure (by using immunoblotting techniques) and spectroscopic characteristics (by using absorption and fluorescence spectra). The sPCP from S. kawagutii is comprised exclusively of a monomeric apoprotein of 35 kDa, whereas sPCP from S. pilosum possesses only a dimeric apoprotein with subunits of 15 kDa each. The sPCP from S. microadriaticum simultaneously contains both. Spectroscopically, sPCP from S. kawagutii is very similar to the 35 kDa species in S. microadriaticum; sPCP from S. pilosum is similar to the 15 kDa species from S. microadriaticum. Gaussian deconvolution analyses of absorption and fluorescence emission spectra show that each holoprotein is comprised of two spectrally distinct forms of chlorophyll a. We propose molecular topologies for sPCP consistent with our findings.